The present invention relates to a mobile communication system.
In a mobile communication system, communication for line connection is performed between a radio base station and a terminal. At this time, it is desirable that the radio base station has large coverage (communication range) and high throughput (communication speed) in terms of efficiency and quality of communication.
A method employed to implement this demand is to increase the output power of the radio base station in a downlink from the radio base station to the terminal. Increasing the output power increases the power consumption, so a device which consumes power as low as possible tends to be used.
Regarding the installation of the radio base station, on the other hand, a compact and light weight radio device is required. In some cases, for this a device in which a redundant configuration of an internal panel of the device is omitted may be used. Communication equipment, however, must have a redundant configuration to effectively be used even in such emergencies as a disaster.
In such a case, a cell redundant configuration may be used. However, if a cell redundant configuration is used, deterioration of connection quality and deterioration of throughput (degenerated operation), which never occurs in a redundant configuration of the internal panel of the device, may occur.
Hence various cell redundancy methods which minimize such deterioration of connection quality and deterioration of throughput have been considered.
An example is the invention according to Patent Document 1. The invention of Patent Document 1 is a code division multiple access (CDMA) system, wherein a frequency band to be used is divided into a plurality of bands, a cluster is constructed by a number of cells which are the same as the number of the division, and interference from adjacent cells is eliminated using this cluster as a unit of using a surface repeat of the frequency, whereby processing for control can also be decreased.
Decreasing interferences from adjacent cells by performing zone repeat is a generally known technology. The invention according to Patent Document 1 is characterized in that this generally known technology is applied to the CDMA system.
Another known technology is an invention according to Patent Document 2. In this invention, an applicable area is covered by a large zone, and if a high traffic area exists in this large zone, the radio base station is disposed so that the small zone of the high traffic area is covered (overlaid).
At this time, it is assumed that the frequency allocated to the large zone is fa, and the frequency band allocated to the small zone is fb, and these frequency bands are divided, for example, into 12 (fa1 to fa12, fb1 to fb12) respectively. In the large zone, fa1 to fa12 are used repeatedly every 12 cells, and in the small zone, fb1 to fb12 are used repeatedly every 12 cells. If the entire applicable area consists of only small zones, the number of radio base stations to be required increases, and if the entire applicable area consists of only large zones, reallocation of the frequency band must be considered, and service must be stopped for a long time when radio base stations are added.
Therefore the invention according to Patent Document 2 is not characterized simply by way of repeating zones, but by way of a cell redundancy configuration.
Patent Document 1: Japanese Laid-open Patent Publication No. H6-104820
Patent Document 2: Japanese Laid-open Patent Publication No. H4-336822